By Steven Cline PhD
Emerald ash borer (EAB) has not hit our state yet but few have any doubt that it will. Several of our neighbor states can attest to the devastation that this Asian-native insect can cause to all native and ornamental ash. More than 15 to 20 million ash have died in Michigan, Ohio, and Indiana with a dollar loss that exceeds $20 billion. Last year, it spread to northern Illinois and Pennsylvania. The most alarming aspect of emerald ash borer is the fact that once a tree is infested, there seems to be no stopping it until the tree dies. The best defense is to be on guard and learn what to look for as you survey your landscape trees. Far quicker than Dutch elm disease, this one will take a healthy tree out in one year.
EAB, as it’s called in the entomological world, was first detected in southeastern Michigan around the Detroit area in the summer of 2002 – probably a transport from wood packing material on cargo ships or planes. The adult is a small, slender emerald green winged insect less than a half-inch long. These adults may cause minor leaf-feeding damage on ash. However, it’s the larvae, a cream-colored, segmented worm, that does the damage, boring into the bark of ash and feeding on the outermost wood layer where life-demanding water and nutrients flow. The feeding behavior is very active as it chews S-shaped tunnels throughout this surface layer. The net result is a girdled, water-starved tree that drops its leaves and dies back, typically from the top down. Unlike other killer diseases and insects that are here already like pinewood nematode, oak wilt, and Dutch elm disease, EAB has no preference for weaken or stressed trees. A young tree is just as susceptible as an old tree; healthy or not.
You might question whether this is the beginning of the end of ash trees in North America. Like chestnut blight that essentially wiped out all of this forest tree, we have set ourselves up because ash is planted widely as an urban tree valued for its tolerance to adverse conditions like compacted soils and drought. Monocultural plantings of ash are everywhere, schools, parks and lining streets, so the impact of an aggressive insect like EAB will be impressive when it gets here. What do we do? The Missouri Department of Conservation, Missouri Department of Agriculture, and US Forest Service took the first step by annual surveys of campgrounds and recreation areas in Missouri since 2005. So far for what is known, we have escaped. The likelihood of spread is most dependent upon the transfer of infested firewood from out of state. There is much more to know and you could help by learning the signs of EAB infestation. Go to Emerald Ash Borer Kills Ash Trees, set up by the Missouri Department of Conservation. Early reporting of this insect’s activities might save this tree as we learn more about chemical and biological control.